A side seamless can be produced, according to a conventional method, by subjecting a metal blank such as an aluminum plate, a tin plate or a tin-free steel plate to at least one drawing stage. The drawing stage is conducted between a drawing die and a punch to form a cup comprising a barrel portion free of seams on the side surface thereof and a bottom portion integrally connected to the barrel portion which is also free of seams. Then, if desired, the barrel portion may be subjected to ironing between an ironing punch and a die to reduce the thickness of the barrel portion of the container. It is also known in the art to reduce the thickness of the side wall by bending and elongating the side wall at a curvature corner part of the redrawing die as described, for example, in JP-B-56-501442 (the term "JP-B" as used herein means an "examined Japanese patent publication").
Methods for coating an organic film onto the side seamless can include a method of applying an organic paint onto a formed can which is a common and widely used technique and, in addition, a method of laminating a resin film onto a metal blank before a can is formed. Furthermore, JP-B-59-34580 describes a product obtained by laminating a polyester film derived from terephthalic acid and tetramethylene glycol onto a metal blank. Also, in the production of a can redrawn by bend-elongation, the use of a metal sheet coated with a vinyl organosol, epoxy, phenolic, polyester or acryl resin is known.
Furthermore, it is known to produce a colored seamless can having an outer face that is coated with a resin film havin previously incorporated therein a coloring agent. JP-B-U-6-16739 (the term "JP-B-U" as used herein means an "examined Japanese utility model publication") and JP-B-U-6-16740 describe a seamless can comprising a laminate of a clear polyester-base molecular orientated film layer/adhesive/surface treated steel plate/adhesive/titanium dioxide-containing polyester-base molecular orientated film/printed ink layer/finishing varnish layer in this order from the inner side to the outer side of the can. Also disclosed is a seamless can comprising a laminate of clear polyester-base molecular orientated film layer/adhesive/surface treated aluminum alloy plate/adhesive/titanium dioxide-containing polyester-base molecular orientated film/printed ink layer/finishing varnish layer, respectively.
JP-A-6-39980 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes a polyester film for use in laminating and forming metal sheets, obtained by laminating a specific copolymer polyester layer containing 1 wt % or less of a lubricant having an average particle size of 2.5 .mu.m or less and a specific copolymer polyester layer containing from 5 to 30 wt % of a filler having an average particle size of 2.5 .mu.m or less.
JP-A-8-3334 describes a metal sheet laminated white polyester film having a Young's modulus of from 50 to 350 kg/mm.sup.2, obtained by laminating a layer comprising polyester (III) mainly consisting of ethylene terephthalate having a melting point of from 150 to 230.degree. C. on a layer which comprises a mixture of polyester (I) containing 20 mol % or more of a cyclohexylenedimethylene terephthalate unit and polyester (II) mainly consisting of ethylene terephthalate in a weight ratio of from 100:0 to 10:90 and containing from 15 to 50 wt % of a coloring agent.
The titanium dioxide-containing polyester-base molecularly orientated film layer arranged on the outer face of a seamless can is advantageous in that it covers the chromium surface treated layer to accentuate the printed ink layer, provides good transmission of a blank holder force on drawing-redrawing to prevent generation of wrinkles on the can barrel, and helps to prevent rusting. However, the following problems still need to be overcome.
In order to enhance the hiding power of the coloring agent particle-containing resin outer layer, the content of the coloring agent particles such as titanium dioxide must be increased. However, if the coloring agent particle content is increased, a problem arises in that the outer layer resin film is shaved, or the forming tools are abraded on drawing formation or ironing formation. This tendency becomes more pronounced as the can barrel portion is thinned to a greater extent so as to save materials or lighten the weight.
In general, the ironing ring is made from a carbide material such as tungsten carbide, and even the carbide material may form a break on the order of several microns after forming a large number of cans. If a tool bears such a break, the seamless can may have a bottom recession, the formed can may not be smoothly stripped from the punch, or the barrel may be broken.
In the process of making a can using a resin laminate sheet, the can is generally filled with contents without rinsing the can barrel after formation. If the film is shaved as described above, the metal can not only has an impaired appearance, but also the film dust may disadvantageously mix with the can contents.